The invention relates to ultrasonic imaging systems and, more particularly, to a drive system for an ultrasonic transducer probe electrically coupled to an ultrasonic imaging system.
The users of medical ultrasonic transducer probes, hereinafter referred to as sonographers, can obtain images of a region within a body by properly positioning a probe against the body. In order to obtain images having diagnostic value, the sonographer may have to physically manipulate the position of the probe by sliding, rotating, and tilting the probe. In one particularly challenging application, the sonographer positions a transducer scanhead at the tip of a transesophageal probe against the esophagus or stomach of a patient in order to obtain different fields of view of the heart.
Typically for this application, the transducer scanhead contains a number of acoustic transducer elements, which may be sequentially electrically excited by an ultrasound system to obtain an image in an object plane that is perpendicular to the scanhead and the transducer elements. It has been found desirable to rotate the transducer elements contained within the scanhead independently from the physical manipulation of the scanhead itself. By rotating the transducer elements, the object plane may be rotated in space about the axis of rotation of the transducer elements.
Devices are known that utilize a drive system to rotate an array of transducer elements. For example, an electric motor may be used to rotate the array of transducer elements with a position encoder, such as a potentiometer, coupled to the motor shaft to provide information on the position of the array of transducer elements. The position encoder may provide either an absolute or an incremental position of the rotatable array. The absolute position encoder can provide the actual position of the array at all times. The incremental position encoder, on the other hand, can provide the relative position of the array with respect to a particular reference position, such as the position of the array at the mime the ultrasound system is powered up.
A disadvantage of devices that utilize absolute position encoders is that such devices may be large and relatively heavy. In addition, analog absolute position encoders, such as potentiometers, may drift with temperature variations and time. It is desirable to minimize the size and weight of such drive systems as well as to provide position information that is stable over temperature variations and time.
A disadvantage of devices that utilize an incremental position encoder is that a rigid rotary stop may be utilized to establish a "home" or reference position. In an overtorque situation, the motor may drive the load into the stop at high speeds causing high shock loads and jamming the drive system.
Accordingly, it would be desirable to have an improved drive system for an ultrasonic probe.